A communication scheme, which is the next generation of a WCDMA (Wideband Code Division Multiplexing Access) scheme, an HSDPA (High-Speed Downlink Packet Access) scheme, an HSUPA (High-Speed Uplink Packet Access) scheme and the like, that is, an LTE (Long Term Evolution) scheme has been discussed in the 3GPP, which is a standardizing group of the WCDMA, and specifying work of the LTE scheme has been conducted.
As a radio access scheme in the LTE scheme, an OFDMA (Orthogonal Frequency Division Multiplexing Access) scheme has been defined for a downlink, and an SC-FDMA (Single carrier Frequency Division Multiplexing Access) scheme has been defined for an uplink.
The OFDMA scheme denotes a multicarrier transmission scheme in which a frequency band is divided into a plurality of narrow frequency bands (subcarriers), and data is loaded on each subcarrier for transmission. According to the OFDMA scheme, subcarriers are densely arranged on the frequency axis while being orthogonal to one another, so that high-rate transmission is achieved, resulting in the improvement of frequency use efficiency.
The SC-FDMA scheme denotes a single carrier transmission scheme in which a frequency band is divided for each terminal, and transmission is performed using different frequency bands among a plurality of terminals. According to the SC-FDMA scheme, since it is possible to easily and efficiently reduce inter-terminal interference and suppress variation in transmission power, the SC-FDMA scheme is preferable in terms of low power consumption of a terminal, expansion of coverage and the like.
In the LTE scheme, communication is performed by allocating one or more RBs (Resource Blocks) to a mobile station in both a downlink and an uplink.
A base station device determines a mobile station, to which a resource block is to be allocated among a plurality of mobile stations, for each subframe (lms in the LTE scheme) (this process will be called “scheduling”).
In a downlink, the base station device transmits a shared channel signal to a mobile station, which is selected through the scheduling, by using one or more resource blocks. In an uplink, the mobile station selected through the scheduling transmits a shared channel signal to the base station device by using one or more resource blocks.
In addition, the shared channel signal is a signal on a PUSCH (Physical Uplink Shared Channel) in terms of an uplink, and is a signal on a PDSCH (Physical Downlink Shared Channel) in terms of a downlink.
Furthermore, in the LTE scheme, for initial connection and the like, Random Access is used. A channel for the random access is called a PRACH (Physical Random Access Channel).
Furthermore, the mobile station transmits a random access preamble via the physical random access channel.
Furthermore, as a communication scheme which is the next generation of the LTE scheme, an LTE-Advanced scheme has been discussed in the 3GPP.
In the LTE-Advanced scheme, performing “Carrier aggregation” has been agreed as the requirements. Here, the “Carrier aggregation” represents that communication is simultaneously performed using a plurality of carriers.
For example, when the “Carrier aggregation” is performed in the uplink, since the mobile station performs transmission using different carriers for each “Component Carrier”, it represents that an uplink signal is transmitted using a plurality of carriers. Furthermore, it has been discussed that multicarrier transmission is performed even in one “Component Carrier”.
In addition, the multicarrier transmission represents that two or more single carrier transmissions are simultaneously performed.
For example, in a component carrier configured by 100 resource blocks, when performing single carrier transmission using 20 resource blocks, it is regarded as single carrier transmission. However, when simultaneously performing two single carrier transmissions of the above-mentioned 20 resource blocks, it is regarded as multicarrier transmission.
In the latter case, a UE performs transmission using a total of 40 resource blocks in a system band configured by 100 resource blocks. Furthermore, in the latter case, even when single carriers including the 20 resource blocks are adjacent to each other, it is also regarded as multicarrier transmission.
Furthermore, in the above-mentioned example, one component carrier exists. However, even when two or more component carriers exist and a plurality of single carrier transmissions are simultaneously performed in the two or more component carriers, it is also regarded as multicarrier transmission.
However, a cellular phone system, a radio astronomy system, a satellite communication system, an air/sea radar system, an earth resources survey system, and a radio LAN system, which are systems using a radio wave, generally separate frequency bands to be used in order to prevent mutual interference. Furthermore, for example, among frequency bands allocated for a cellular phone system, frequency bands allocated for a plurality of systems exist, and frequency bands of each system are separated from each other.
That is, a system using a radio wave separates frequency bands to be used, thereby preventing inter-system interference.
However, since a transmitter radiating a radio wave radiates an unnecessary wave (hereinafter, referred to as adjacent channel interference) in an outer band of a frequency band of an own system, although a frequency band has been separated, mutual interference occurs among a plurality of adjacent systems. Therefore, when a power level of the unnecessary wave is high, it has a significant adverse influence on adjacent systems.
In order to prevent the adverse influence on the adjacent systems due to such adjacent channel interference, performance related to characteristics related to the above-mentioned adjacent channel interference and spurious emission is defined in each system.
However, in order to suppress the unnecessary wave to the outer band of the frequency band of the above-mentioned own system, the mobile station should be provided with a power amplifier with high linearity.
Therefore, when considering the cost and size of the mobile station, it may be difficult to reduce the above-mentioned unnecessary wave or satisfy the regulations of the above-mentioned adjacent channel interference and spurious emission.
Reducing maximum transmission power is called “Maximum power reduction (MPR)”. For example, in the LTE scheme, the MPR is defined on the basis of a modulation method, a system bandwidth, and the number of resource blocks. The maximum transmission power is reduced in this way, so that it is possible to further reduce the cost and size of the mobile station.
As described above, the LTE-Advanced scheme, which is the next generation of the LTE scheme, has been currently discussed in the 3GPP. In the LTE-Advanced mobile communication system, a mobile station can transmit an uplink signal through a multicarrier using a plurality of transmission antennas or transmitters. Furthermore, even when using one transmission antenna or transmitter, the mobile station can transmit the uplink signal through the multicarrier.
However, in the LTE-Advanced mobile communication system, when the mobile station has transmitted the uplink signal through the multicarrier using the plurality of transmission antennas or transmitters, a problem may occur in which an interference amount to frequency bands of adjacent systems is increased, as compared with the case in which the mobile station has transmitted the uplink signal through a single carrier using one transmission antenna or transmitter. The problem also exists in the case in which the uplink signal is transmitted through a multicarrier using one transmission antenna or transmitter.
Therefore, the present invention has been achieved in view of the above-described problems, and an object thereof is to provide a user equipment, a base station device, and a communication control method, which can reduce an interference amount to frequency bands of adjacent systems even when transmitting an uplink signal through a multicarrier using a plurality of transmission antennas or transmitters, or one transmission antenna or transmitter.